Document Sample

                                               Guy Snelling
                                       PO Box 10907 Vorna Valley 1686


Steam autoclaves have been with us for many
years and are used in many different industries.
Their primary task is to sterilize items so that
these same items can be used in situations
where the introduction of micro-organisms
would pose a health-risk. But how can we be
sure that the autoclave is doing its job?
Biological indicators form part of this validation,
but there are many tests that should be
performed regularly. This paper describes
these tests, and how often they should be
performed in order for the user to be confident
that their autoclave is functioning properly and
within the requirements of the regulatory

                  Introduction                                               Figure 1
                                                              Diagram of a horizontal steam autoclave
There are four general types of sterilizers
namely, Gamma Irradiation, Gas Sterilization,            An alternative method is used in vertical
Dry Heat and Moist Heat. Whilst validation of            autoclaves. See figure 2. Water is placed in
all types of sterilizers follows the same basic          the bottom of the chamber and heated by an
principles, by far the most prevalent type in            electrical element. The resulting steam drives
South Africa are steam or moist heat                     the air out of an evacuation port near the top of
autoclaves and this paper therefore deals                the chamber. Again the evacuation port is
specifically with this type.                             closed once all the air has been removed and
                                                         the steam pressure is allowed to build.
             Method of Operation

Steam autoclaves generally follow the
principles shown in Figure 1. Water is heated
and the steam pressure is built up in the jacket.                                        valve
Once sufficient pressure is obtained, the steam
is allowed to enter the chamber, thereby driving
the air out of the drain port. Once all the air
has been replaced by steam, the drain valve
closes and steam pressure builds up in the                                               Steam
chamber. The resultant pressure causes the
temperature in the chamber to rise to the
required point, usually 121 or 135 °C.

Some type of autoclaves have a vacuum                                                  Element

function that pumps out the air before the
steam is allow to enter. This method is much
faster and more efficient.                                    Figure 2 Diagram of vertical autoclave
                  Cycles Stages

Generally an autoclave cycle consists of 3                          Load Types
stages viz. heating, sterilizing, de-pressure.
Vertical autoclaves may have a “water fill”       Autoclaves are used         to   sterilize   several
stage before the heating stage. Autoclaves        different types of loads:
fitted with vacuum facility may have vacuum
stages before the heating stage and also as               Solid – metal, glass, plastic
part of the depressurizing stage.
                                                          Porous – linen, gowns, paper, gauze,
                                                          complex instruments, hollow tubes

                                                          Liquid – water, saline, media

                                                          Laboratory waste – Petri dishes,
                                                          sample bottles, syringes         [1]

                                                  There are various methods of validation,
   Heating Sterilizing Depressure Complete        depending on the usage of the autoclave.


        Figure 3 Typical autoclave cycle          The instrumentation fitted to an autoclave will
                                                  vary depending on the complexity and price of
                 Why Validate?                    the autoclave. A vertical autoclave may only
                                                  be fitted with a pressure gauge (also marked
                                                  in ° C) and a pressure regulator. A more
                                                  complex, fully automated large autoclave may
                                                  have a computer controlled display showing
                                                  various temperature and pressures throughout
                                                  the workings of the autoclave. Typically though,
                                                  jacket pressure and chamber pressure would
                                                  be indicated, along with chamber temperature.

                                                  Validation requires that these instruments be
                                                  checked for accuracy.

                                                                 System supplies

                                                  Most autoclaves are electrically powered and
                                                  all steam autoclaves require some form of a
                                                  water supply to produce steam. The electrical
                                                  supply must be able to handle the maximum
                                                  peak power of the autoclave. The quality of the
                                                  water supply will affect the quality of the steam

                                                  The drainage system must be able to handle
 Figure 4 Temperature and Physical Control of     the maximum flow of water and condensate
              Microorganisms                                                          C.
                                                  and should be able to tolerate 100 ° [1]

As can be seen from Figure 4, if the
temperature in an autoclave does not reach
121 ° not all spores will be destroyed in the
typical cycle time of 20 minutes. Validation is
therefore required to ensure that the autoclave
is operating correctly and that complete
sterilization is being achieved.
                  Validation                                  that both water quality and steam
                                                             quality comply with the sterilizer
Validation is described as a documented                      specification
procedure for obtaining, recording and
interpreting data required to show that a                    the chamber is capable of withstanding
process     will consistently     comply with                its specified maximum pressure. This
predetermined specifications. [3]                            test may be a legal requirement and
                                                             should be performed by a suitably
In the case of autoclaves the validation process             certified organisation.
may be broken down into the following tests:
                                                               Performance Qualification
       Installation Checks                           The performance qualification (PQ) tests
       Installation Tests                            actually check that the autoclave is not only
       Commissioning Tests                           functioning correctly, but also that sterilization
Performance Qualification                            is taking place. Analysis of documented PQ
       Thermometric Tests                            results can also assist with pro-active
       Microbiological Tests     [1]                 maintenance schedules.

According to EN554:1994 “Sterilization of            A thermometric test to determine the
medical devices – Validation and routine             temperature profile inside the chamber
control of sterilization by moist heat” [3], the     throughout the holding time, using a data
Commissioning tests need only be performed           logging system and multiple probes placed
at initial installation and after certain repairs    throughout    the     chamber      volume.
while the Performance Qualification tests            Simultaneous monitoring of the chamber
should be performed regularly and routinely.         pressure is also useful in checking the
                                                     efficiency of the air removal/replacement
               Commissioning                         system.

“Commissioning: Obtaining and documenting            Once qualification of the empty chamber has
evidence that equipment has been provided            been accepted, load testing should be
and installed in accordance with its                 performed. Here, similar probes as used in
specification and that it functions within pre-      monitoring the temperature profile, are placed
determined limits when operated in accordance        inside typical loads and the heat transfer time is
with operational instructions” [3]                   determined during the sterilization cycle.
                                                     These tests should be repeated for each type
Commissioning tests should include checking:         of load and/or preprogrammed cycle that for
                                                     which it is intended to use the autoclave.
        that the electrical supply is suitable for
        the autoclave                                During the load testing, biological indicators
                                                     may also be placed in the load to determine if
        that the temperature and humidity are        sterilization is in fact taking place.
        sufficiently well controlled
                                                     If the autoclave is to be used to sterilize folded
        that there is no interference to or from     cloth, such as garments, a Bowie Dick test
        other equipment                              should be performed to ensure complete
                                                     penetration of the steam into the cloth.
        the accuracy of indicators has been
        certified to national standards                          Maintenance intervals

        the temperature and pressure of the          The      intervals    between      Performance
        chamber during a sterilization cycle are     Qualification tests should be determined based
        within specifications                        on documented experience and the need, type
                                                     and previous performance of the autoclave.
        the leakage into the chamber during a        EA-4/10 “Accreditation in Microbiological
        vacuum cycle does not exceed the             Laboratories”     suggests    that  the   load
        specified maximum                            characteristic for each cycle be determined
                                                     every two years, while the chamber
        that there is no leakage of steam, water     temperature and time must be monitored during
        or effluent at any point during the          each use. [2]
        sterilization cycle
Regular maintenance such as gasket                    performance qualification tests should be fully
inspection, and cleaning of the chamber should        recorded, reviewed, accepted and archived by
be     performed     at   the     manufacturers       the relevant personnel in the organisation that
recommended intervals. A full service should          uses the autoclave.
be performed at least annually as should the
safety check of the pressure vessel.                  These results may be recorded on suitable
                                                      worksheets and certificates may be issued by
Any repairs or modifications of the unit may          third-party organisations that perform such
require complete, or at least partial, re-            tests.
commissioning of the autoclave, including full
Performance Qualification tests.

               Routine Checking                                          Conclusion

Routine checking may be broken down into              The      commissioning        and    performance
daily, weekly, quarterly and annual checks.           qualification of an autoclave and subsequent
                                                      validation of the sterilizing protocols is a costly
Daily checks should be performed by the               and time consuming process, both in the actual
operator and should include the observation of        procedures involved and also in the analysis
all indicators for “normal” values.                   and review of the resulting documentation.

On a weekly basis safety checks should be             Ensuring that sterilization is occurring in the
performed such as inspection for leaks and            autoclave is however of prime importance
electrical wiring faults, inspection of door seals,   (otherwise why bother to autoclave in the first
correct of operation of door interlocks and high      place) thus such costs should be viewed in the
temperature and low water alarms. In the case         light of human safety rather than that of
of vacuum autoclaves, a vacuum leak test              economics.
should also be performed.
                                                      At the same time, however, to ensure that
Quarterly checks may include verification of the      qualification and validation are performed
calibration of the instrumentation, a check of        correctly, the tests should only be carried out
the automatic control functions, a check of the       by suitably qualified and experienced personnel
vacuum leak sensor and a thermometric test on         and organisations.
a small load.
Annually, a full re-commissioning may be              [1]   A. Chandler, Introduction to Sterilization
warranted. Thermometric testing should be
performed. Load testing should be performed           [2]   European co-operation for Accreditation
as well, but different loads may be scheduled               EA-04/10 Accreditation for Microbiological
into bi- or tri-annual cycles. [1]
                                                            Laboratories, July 2002 rev02
                                                      [3]   European Committee for Standardization
                                                            EN 554:1994 Sterilization of medical
                Documentation                               devices – Validation and routine control of
                                                            sterilization by moist heat, June 1994
The results of all commissioning tests and